This invention relates to a remote control system having a portable remote control unit for controlling at least one function unit, and a bidirectional data communication path for transmitting symmetrically encoded data between the remote control unit and the function unit, and to an operating process for such a system.
Code protected remote control systems of this type are used, for example, for motor vehicles and external motor-vehicle-related devices, such as garage door openers, to limit access to a selected group of authorized users. Authorized users establish their usage authorization to the respective controllable function unit by the fact that they are in the possession of an authorizing remote control unit. The remote control unit triggers a bidirectional code data exchange in which the pertaining authorization code is transmitted between the two units in a coded manner, and is subsequently examined for its conformity and therefore usage authorization. The use of a symmetrical coding method, which presupposes the presence of identical secret coding information in both units, offers a high degree of protection against attempts by unauthorized persons to control the function unit themselves, after having listened to such a code data exchange.
German published patent application DE 32 25 754 A1 discloses a remote control method and apparatus of this type, in which the secret coding information of the symmetrical coding method is a mathematical function, which is stored in an identical and unchangeable manner, on the one hand, in a key part and, on the other hand, in a lock part.
In cryptography, the so-called DES (Data Encryption Standard) algorithm is known, among others, as a very safe algorithm for symmetrical coding methods. German patent document DE 44 11 450 C1, for example, discloses a vehicle safety device with an electronic usage authorization coding for implementing a replacement key, instead of an asymmetrical coding method for a protected code data exchange in which only one of the two mutually communicating units must contain secret coding information.
In various cases, it is known to use a portable remote control unit in the form of an electronic vehicle key. The key not only authorizes access and/or usage of a motor vehicle, but also controls other vehicle function units or other function units, such as a garage door opening. For this purpose, in a representative manner, reference is made to German patent documents DE 30 43, 627 C2, DE 40 18 261 C1 and DE 42 15 221 C2 as well as to German published patent application DE 40 03 280 A1.
German published patent application DE 41 02 020 A1, discloses a remote control system having a vehicle key which is configured for bidirectional information exchange with the vehicle to control locking and unlocking elements of the vehicle. In addition, it also has a visual display unit for displaying information concerning driving condition parameters transmitted from the vehicle, such as the condition of the vehicle doors, driven mileage and level in the fuel tank, as well as additional non-vehicle parameters, such as the time of day and the condition of the key battery.
European published patent application EP 0 617 183 A2, discloses a vehicle remote control system with a key that has a voice memory, a microphone and a voice playback unit. Information, such as the number of a parking space where the vehicle is situated, can be fed in voice form into the key and stored there, after which this information can be retrieved from the key in voice form by the user.
Published patent application WO 90/15211 describes a remote control system of the initially mentioned type, for transmitting data which contain a random number, coded for example by means of the DES coding method, between the remote control unit and the function unit. The pertaining secret coding information can be changed in the remote control unit by bringing the latter together with an additional coding unit into which the user must first input the previous secret coding information to prove his authorization. If the code conformity test is successful, the user can feed new secret coding information into the remote control unit by way of the coding unit. The transmission of the new secret coding information into the function unit takes place after a normal authentication operation in which a negative result has occurred because of the secret coding information, which so far has been changed only in the remote control unit. The function unit will then change to a learn mode and, by way of the DES coding method, will retrieve the new secret coding information from the remote control unit.
In the remote control system described in U.S. Pat. No. 4,988,992, authorization codes of at least one. remote control unit can be transmitted to at least one function unit. In order to change the respective authorization code as required, the corresponding remote control unit is first brought into a programming mode which activates a random code generator provided there. The random code is stored in the remote control unit as a new authorization code. Additional remote control units can be synchronized by activating a learn mode, in which they can receive the new authorization code from the newly programmed remote control unit by way of a special antenna, if the remote control unit is brought into the direct vicinity and is caused to send the new authorization code. For entering the new authorization code into the respective function unit, a programming mode is activated on it, after which the function unit will, for a given time period, be enabled to receive a new authorization code which does not correspond to its previously stored code. A code received within this time period will then be stored by the function unit as a new authorization code.
One object of the invention is to provide a remote control system and process of the initially mentioned type which requires relatively low expenditures, and in which the secret coding information used for the applied symmetrical coding method can be changed in a simple manner that is protected from manipulation.
This problem is solved by means of a remote control system according to the invention, in which the learning operation for replacing previous secret coding information with new secret coding information is both simple and secure. When the learn mode is activated, the remote control unit automatically calculates new secret coding information, preferably by means of a pseudorandom operation. Since the secret coding information remains hidden even to the rightful owner of the remote control unit, he is not burdened with inputting it. Because new secret coding information can be generated upon request, the learn mode can be repeated as often as desired for the purpose of selecting new secret coding information. Because of the learning activation, and because the secret coding information can be replaced only in the function unit, after acknowledgment of secret coding information by the function unit to the remote control unit, it is ensured that the generation of new secret coding information triggered by an unauthorized person, on the one hand, remains useless to him (since the function unit continues to require control by means of the old secret coding information) and, on the other hand, the authorized user will be able to continue to control the function unit by means of the remote control unit on the basis of the old secret coding information, which remains valid. Alternatively, it is also possible to preclude the generation of new secret coding information in the remote control unit when the function unit is not activated. The function unit should be guarded against access by unauthorized persons, and activation of the learn mode at the function unit should be protected by suitable locking; for example, by means of a key switch.
In one embodiment of the invention, at least one vehicle-side function unit (such as an auxiliary heater) and at least one function unit outside the vehicle (such as a garage door opener) can be controlled by the remote control unit. Furthermore, in a reversed data transmission direction, condition information, particularly with respect to the respective function unit, can be transmitted to the remote control unit and can be indicated there visually and/or acoustically.
In another embodiment, separate secret coding information for the coding algorithm in the remote control unit is assigned to each of the function units which can be controlled by the remote control unit. Thus, the secret coding information for various controllable function units can be changed independently of one another.
In still another embodiment, the controllable function unit can be switched between several learn mode channels, each of which is used to establish secret coding information for data communication with a specific remote control unit. In this manner, the function unit can be controlled by several authorizing remote control units, each with respective specific secret coding information.
Finally, in yet another embodiment of the invention, the so-called DES (Data Encryption Standard) algorithm for the symmetrical coding method is used. This arrangement permits particularly secure data communication between the remote control unit and the controllable function unit, at expenditures which are acceptably low.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.